This invention is suitable for the performance of a die bonding process in manufacturing a semiconductor member, and relates to a method of positioning, by examining the semiconductor members, each qualified one thereof at a prescribed position and to a die bonding apparatus using the said method.
To precisely perform a die bonding process in manufacturing a semiconductor member, it is generally necessary first to examine such semiconductor members, i.e., pellets, disposed, in orderly arrangement and at appropriate intervals, on a transparent sheet pasted onto a wafer cassette and then to move with precision only each qualified one of the pellets, that is, to position it with precision. By being precisely positioned as such, the pellet is precisely picked up by a pellet picking-up mechanism and is carried to a prescribed position on a lead-frame and thus is secured thereto. Accordingly, the next process, for example, a wire bonding process, can be conducted with precision.
Conventionally such method of examining the qualification or non-qualification of pellets and precisely positioning each of pellets at a prescribed position, as mentioned above, is already contemplated and reduced to practice. There does not exist, however, any easily manipulatable and highly reliable apparatus for sequentially automatically examining with high precision a large number of pellets loaded on a wafer cassette and positioning each pellet at a prescribed position.
A conventional apparatus is outlined as follows. That is, one of the methods used to examine the qualification or non-qualification of pellets and position each qualified one thereof comprises the step of moving, while an operator is microscopically observing a pellet, such pellet to a prescribed position defined within a visual field of the microscope, and visually examining the qualification or non-qualification of the pellet during the pellet moving operation. But this method has the drawback that such examining and positioning operation is very tiresome and yet requires a high level of skill. Thus there has been a demand for other methods, especially for automatization of such an examining and positioning operation.
In accordance with the above-mentioned demand, a wide variety of automatizing methods have heretofore been contemplated. In automatization of the pellet examining and positioning method, a method using a television camera has been proposed as one such examining and positioning method. One of such television camera using method is an invention of Japanese Patent Application Publication No. 1689/73 as filed in Japan, entitled "A method of positioning articles and an apparatus therefor". Generally, the automatization of this type of positioning operation is performed by using the method of converting into a digital signal an image signal photographed by a television camera and processing the digital signal by operation of an electronic computer or an operation processor circuit similar thereto, thereby to calculate the amount of displacement of an article or substance from a normal or correct position therefor. In this case, however, in order to convert said image signal into such digital signal, the sampling of the image signal has to be performed. Since the scanning speed by the camera is remarkably high, a circuit for such sampling also has to have a very high-speed performance. Further, a considerably high level of technique is required to supply the sampled signal data into said computer or operation processor circuit. As a result, the apparatus itself using such method becomes costly, and entry or mixing of noises thereinto becomes likely to occur. This apparatus, however, has various drawbacks including those that the constituent parts of the apparatus are likely to be thermally changed due to heat generation from a television camera to cause an occasional change with time of the light axis; that the television camera is operated in accordance with analogue signals to cause an easy entry or mixing thereinto external noises and also to cause an easy occurrence of a drift phenomenon; that the pellet positioning can not quickly be carried out owing to the existence of residual images on the photoelectric face of an image pickup tube; that since the scanning direction of scanning lines of the television camera is fixed, a complicated circuit is required to obtain signals denoting the position of a two-dimensional article; and that a television camera providing a large number of scanning lines is required to be used for close detection of an article position, resulting in a high cost of such television camera. Therefore, the above apparatus can not be said to sufficiently fit the practical use from the standpoints of positioning precision, operating efficiency, expenditures, etc.
Further, in addition to such apparatus using a television camera as mentioned above, another examining and positioning method has been contemplated which comprises projecting the enlarged image of a pellet on a screen, detecting in analogue manner the edge portions of the enlarged projected image by means of photoelectric conversion elements, such as solar batteries, disposed on the screen, and moving the pellet so as to permit the resulting detection output to become a prescribed value, thereby to perform the positioning of the pellet. However, the side faces of a pellet are often not perpendicular to the upper face thereof, and further at the edge portions of the pellet there usually exist irregularities of a considerably large size and number. Therefore, the pellet positioning can not be performed with high precision. This examining and positioning method has further drawbacks. Even in a case where a pellet has damages or breakages causing no inconveniences on the performance of the pellet, it is judged to be a defective pellet or it fails to be precisely positioned. Since in the die bonding process an analogue signal delivered from each photoelectric conversion element is used, in a case where a light intercepting foreign matter such as dust has been adhered to, for example, a vinyl sheet having pellets pasted thereon, precise edge detection becomes impossible.
As above described, any of the conventional methods encounter difficulties in the positioning of a pellet with high precision, and the examining of pellet qualification, necessary to, for example, the die bonding process in the course of manufacturing a semiconductor element.